Engine performance analyzer

ABSTRACT

An internal combustion engine performance analyzer is described for simultaneously displaying certain operating characteristics, such as ignition waveform, horsepower output, etc., under controlled operating conditions. A plurality of probes are coupled to the engine to provide output signals representative of engine performance characteristics such as cylinder ignition, generator output, starter current, etc.. To provide output signals representative of additional operating characteristics, a dynamometer and an exhaust analyzer may also be coupled to the engine. The analyzer includes an oscilloscope and at least one selectable scale test meter in which a rotatable drum positions one of six possible scales adjacent the meter indicator or pointer at a time. A multiple position program switch controls the drum position to provide the proper scale and couples selected output signals from the engine, dynamometer or exhaust analyzer to the meters and the oscilloscope for a selected test procedure. The program switch also couples one of several sweep signals to the oscilloscope so that signals, for example, representing the spark plug voltages of the cylinders may be displayed in a superimposed pattern or separated in a vertical or horizontal pattern on the oscilloscope. The program switch enables the operator to diagnosis an engine by simply rotating the switch through each of its positions and reading the values of the parameters under test on the scales positioned adjacent the meter indicators. The waveforms of a selected parameter such as ignition voltages, starter current, etc., are simultaneously displayed on the oscilloscope for each switch position.

United States Patent Olsen Feb. 5, 1974 ENGINE PERFORMANCE ANALYZER [75]lnventort Dick Merlin Olsen, Pasadena, Calif.

[73] Assignee: Clayton Manufacturing Company,

El Monte, Calif.

[22] Filed: Jan. 28, 1972 [21] Appl. No.: 221,613

[52] US. Cl 73/1173, 324/16 S [51] Int. Cl. GOlm 15/00 [58] Field ofSearch 73/117.3, 116, 117.2, 117', 324/115, 16 S [56] References CitedUNITED STATES PATENTS 3,650,149 3/1972 Howes 73/1173 2,558,276 6/1951Simpson et al.. 324/115 3,446,070 5/1969 Hickox ll6/l36.5 X

3,308,377 3/1967 Lukso et al. 324/115 Primary ExaminerJerry W. MyracleAttorney, Agent, or Firm-Jackson & Jones Law Corporation 5 7 ABSTRACT Aninternal combustion engine performance analyzer is described forsimultaneously displaying certain operating characteristics, such asignition waveform, horsepower output, etc., under controlled operatingconditions. A plurality of probes are coupled to the engine to provideoutput signals representative of engine performance characteristics suchas cylinder ignition, generator output, starter current, etc.. Toprovide output signals representative of additional operatingcharacteristics, a dynamometer and an exhaust analyzer may also becoupled to the engine.

The analyzer includes an oscilloscope and at least one selectable scaletest meter in which a rotatable drum positions one of six possiblescales adjacent the meter indicator or pointer at a time. A multipleposition program switch controls the drum position to provide the properscale and couples selected output signals from the engine, dynamometeror exhaust analyzer to the meters and the oscilloscope for a selectedtest procedure. The, program switch also couples one of several sweepsignals to the oscilloscope so that signals, for example, representingthe spark plug voltages of the cylinders may be displayed in asuperimposed pattern or separated in a vertical or horizontal pattern onthe oscilloscope. The program switch enables the operator to diagnosisan engine by simply rotating the switch through each of its positionsand reading the values of the parameters under test on the scalespositioned adjacent the meter indicators. The waveforms of a selectedparameter such as ignition voltages, starter current, etc., aresimultaneously displayed on the oscilloscope for each switch position.

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flaaess' PATENTEDFEB 51m sum 5 0F 5 ENGINE PERFORMANCE ANALYZERBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an internal combustion engine analyzing system and moreparticularly to an electronic system for analyzing certain engineoperating characteristics.

2. Description of the Prior Art A number of electronic analyzers areavailable in the prior art to indicate various performancecharacteristics of internal combustion engines. Some of theanalyzers areaimed particularly at a diagnostic analysis of the ignition system ofautomobile engines. Other analyzers include means for determininghorsepower output at various engine or automobile road speeds and ananalysis of the exhaust gases to determine the content of certainundesirable gases. These prior art devices generally employ a cathoderay tube oscilloscope to provide a visual display of certain test datasuch as spark plug voltage waveform. The prior art devices also employone or more electric meters for measuring the voltage and/or current.Such electric meters generally utilize a dArsonval type movement inwhich a pointer is moved through a predetermined arc in response to themagnitude of the input voltage or current. A scale behind the pointerpermits the operator to read the value of the parameter being measured.Since many parameters must be measured to determine engine performanceas many as six different scales are positioned behind the pointers ofeach of the meters in the prior art analyzers.

It is often difficult for the test operator to correlate the properscale with the parameter under test. Furthermore, the scales decrease inlength toward the axis of the meter movement thereby decreasing theresolution of the meter. Loss of meter resolution requires larger andmore costly meters if the analyzer is to enable the operator to adjustthe timing and carburetion of the engine with sufficient accuracy tomeet the present high standards of emission control. The meters are alsodifficult to read by the operator when he, of necessity, must be locatedat some distance from the analyzer, for example, in the car controllingthe throttle. Furthermore, the pointers of such prior art meters arepositioned at some distance from the scale providing paralax whichfurther increases the problem of obtaining an accurate reading.

The prior art analyzers not only employ meters which are confusing anddifficult to read, but include a large number of switches,potentiometers, etc., which must be set in the proper position for eachtest procedure. For example, the proper leads from the engine,dynamometer or exhaust analyzer must be coupled to the meters and thesignal input circuit (vertical deflection coil) of the oscilloscope foreach test procedure. Also the proper sweep voltage must be applied tothe sweep circuit (horizontal deflection coil) of the oscilloscope todisplay the data in the proper return. The operation of such prior artanalyzers requires highly trained personnel. Furthermore, the manyadjustments and switch positions under the control of the operatorprovide a large margin for error.

SUMMARY OF THE INVENTION The present invention overcomes thedisadvantages of such prior art analyzers by providing an apparatuswhich is highly accurate and simple to operate. The apparatus includes aplurality of probes coupled to the engine to provide output signalsrepresentative of various engine performance characteristics. Theapparatus also includes an oscilloscope which is provided with a signalinput circuit and a sweep input circuit for providing a visual displayof selected engine characteristics such as spark plug voltages,generator charging current, etc.. Sweep signal generating means arearranged to selectively generate one of a plurality of sweep voltages sothat several signals may be displayed simultaneously on the oscilloscopein a superimposed, horizontally or vertically stacked pattern.

At least one selectable scale test meter is provided with a test signalinput circuit and an indicator movable between two points in response tothe applied signal to provide a measure thereof. The test meter furtherincludes a rotatable drum carrying a plurality of individual scales onthe periphery thereof with one scale positioned adjacent the indicatorand between the two points at any one time. A scale selection circuit isincluded in the test meter with means responsive to signals applied tosuch circuit for rotating the drum to position a selected scale adjacentthe indicator.

The analyzer is controlled by a multiple position program switch whichhas at least first, second and third contact means. The first contactmeans is coupled between selected probes and the test input circuit ofthe meter for applying an input signal to the meter representative ofpredetermined engine characteristics at selected switch positions. Thesecond contact means is coupled between selected probes and the signalinput circuit of the oscilloscope to provide a display representative ofthe selected probe output signals at selected switch positions. Meansincluding the third contact means are provided for connecting the sweepgenerating means to the sweep input circuit of the oscilloscope andcontrolling the sweep output voltage to provide a selected sweep rasteron the oscilloscope for each switch position. Scale selector meansresponsive to each position of the program switch are provided forapplying signals to the meter scale selection circuit for causing thedrum to position a selected scale adjacent the indicator for each switchposition.

The analyzing apparatus of the present invention may be coupled to theengine with simple clips. Oncethe analyzer is initially adjusted toaccommodate the number of engine cylinders, e.g., two, four, six oreight and the polarity of the battery supply, the program switch maythen be sequenced through its multiple positions to provide a completeengine diagnosis. The values of the parameters being tested may bereadily read on the single scale positioned behind the meter indicatorsfor each test procedure. The waveforms of the parameters underobservation, such as spark plug voltages, are also displayed in theproper pattern on the oscilloscope for each test procedure. Theflexibility of the analyzer may be increased by adding a trigger switchfor selecting the primary or secondary ignition coil pulses for visualdisplay and a cylinder select shorting switch to permit the cylinderbalance to be readily checked. The analyzer may be operated byrelatively untrained personnel to provide an accurate engine diagnosisin a minimum of time. The, analyzer is described in more detail inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation of ananalyzer in accordance with the present invention;

FIG. 2 is a partial plan view in schematic form of a selectable scaletest meter for use in the apparatus of FIG. 1;

FIG. 3 is a partial elevational view of the selectable scale test meter;

FIG. 4 is an exploded view of one end of the test meter of FIGS. 2 and3;

FIG. 5 is an enlarged partial perspective view of a program switch foruse in the apparatus of FIG. 1; and

FIGS. 6A and 68 comprise a block diagram of the electronic circuitry foruse in the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, theapparatus of the present invention includes a housing 10, anoscilloscope 12 and three selectable scale test meters 14, 16 and 18mounted in the housing with a selected scale of each meter positionedwithin windows 15, 17 and 19. Each meter includes a movable indicator inthe form of a Mylar tape 20 having a colored portion 21 and atransparent portion 22 with the junction 23 functioning as the indicatorto provide a measure of the input signal as will be described in moredetail. A program switch 24 is provided with a manually actuable knob 25for positioning the switch in any selected position from A-L asillustrated.

The diagnostic apparatus includes a power switch 26 for selecting theproper number of cylinders for the engine under test, e.g., two, four,six or eight. A polarity switch 28 correlates the polarity of thediagnostic apparatus to the polarity connection of the battery of theengine under test. A trigger switch 30 is provided for permitting .thepulses from the primary or secondary winding of the ignition coil to bedisplayed on the oscilloscope 12. A cylinder selector switch 32 permitsthe'operator to short out one of the engine cylinders at a time to testthe power contribution of individual cylinders as will be explained inmore detail. A strobe light unit 34 including a potentiometer adjustmentknob 36 is provided for making conventional timing measurements. Theterm engine as used herein includes such accessories as the battery,starter, generator and ignition system.

FIGS. 2, 3 and 4 illustrate a selectable scale test meter that may beutilized in the apparatus of the present invention. A selectable scaletest meter of this type is the subject matter of a copending applicationMETER WITH ELECTRICALLY SELECTABLE SCALES," Ser. No. 221,667, filed Jan.28, 1972 by Gordon l... Brock. Each test meter 14, 16 and 18 includes atest signal input circuit 40 for applying a test signal to one input ofa differential amplifier 42 as shown in FIG. 2. The other input to thedifferential amplifier is obtained from a movable contact or wiper 44 ofa potentiometer 45. The potentiometer 45 is connected between areference voltage and ground as illustrated. The wiper 44 is coupled toa shaft 46 ofa servo motor 48 which is energized by the output from theamplifier 42. The output shaft 46 of the motor is also connected to atape reel 48 on which is wound a length of the Mylar tape 20. The Mylartape is twisted through 90, passed around a guide roller 49, across theside of a translucent plastic drum 50 which is exposed through one ofthe windows 15, 17 or 19, around a guide roller 51 and to a rotatablestorage reel 52. A spring 53 is fixed at one end relative to the housing10 and is connected at the other end to a flexible cord 54 which iswound around a shaft 55 carrying the reel 52.

In operation, a signal applied to the input circuit 40 energizes themotor 48 which turns the shaft 46 until the voltage on the wiper 44 isequal to the voltage applied to the input circuit 40. Typically theinput signal may vary between 0 and 10 volts to provide a rotation ofthe shaft 46 and reel 48 sufficient to cause the indicator 23 of thetape 20 to travel between two predetermined points located at each endof the drum 50. The spring 53 maintains a constant tension on the tape20 so the tape is wound on the take up reel 52 at the same rate that itis unwound from the supply reel 48 and vice versa. The tape 20 ispositioned almost in contact with the drum 50 to eliminate paralax.

The drum 50 of the test meter is hollow as is best illustrated in FIG. 4and carries six scales spaced at 60 intervals along its periphery. Thedrum is rotatably mounted by end supports 60 and 61 which are secured tothe housing 10 in any suitable manner. The drum 50 carries an end plate62 (FIG. 4) which is provided with six bores 64 spaced at 60 intervals.The plate 62 also carries a bifurcated flexible contact 66 which wipesstationary contacts 67 and 68 on a fixed plate 70. The plate 70 furtherincludes a bore 72 which receives an indexing pin 74 driven by thearmature of a solenoid 76 as shown in FIG. 3. The pin 74 also carries amovable contact 78 which engages stationary contacts 79 and 80 when thesolenoid armature is not energized as illustrated. The solenoid 76 isenergized through a line 82 which is connected to the contacts 67 on thefixed plate 70. The contact 80 is connected to a suitable bias sourcesuch as minus 12 volts. The drum 50 is rotated by a shaft 84 which isconnected at one end to the plate 62 and at the other end to a gear 86.The gear 86 is driven by a gear 88 coupled to a motor 90 via a suitableclutch 89. The motor 90 is energized by the contacts 78-80 when thesolenoid 76 is not energized.

The solenoid 76 is controlled by the program switch 22 which isillustrated in FIG. 5 and comprises a plurality of stationary contactdiscs -107 carrying fixed contacts associated with each switch positionand a rotatable shaft 109 which carries movable contacts 110-117. Themovable contacts 1l0l 17 are insulated from the shaft 109 and areconnected by spring contacts as shown to bias sources, the signal inputcircuits of the three test motors, the sweep generator and the verticaldeflection coil of the oscilloscope, as noted on the drawing. Thestationary contacts of the program switch are coupled to the probes,speed signal or RPM generator and to the scale selection circuits of thethree meters as indicated in FIG. 5.

The position of the drum 50 of each meter is controlled by the programswitch 24. For example, when the program switch is rotated by theposition shown in FIG. 5, the rotating contact 110 engages a fixedcontact on the disc 100 and energizes the line 100A with l2 volts. Theline 100A forms a portion of the scale selection circuit 69 of the meterand is connected, for example, to one or more of the fixed contacts68a-f. Assume that line 100A is connected to fixed contact 68d. At thistime, the solenoid 76 is not energized and the movable contact 78 is inthe position illustrated inFIG. 3 which energizes the motor 90. Themotor 90 rotates the drum 50 until the bifurcated contact 66 engages thecontact 68d and the corresponding contact 67. At this time, the solenoid76 is energized and drives the indexing pin 74 and movable contact 78toward the drum to deenergize the motor 90. The pin 74 is driven throughthe bores 72 and 64 and stops rotation of the drum 50 with the properscale positioned adjacent the indicator 21. The solenoid 76 remainsenergized until the program switch is rotated to a new position at whichtime the drum 50 is again rotated as described above.

Referring now to FIGS. 6A and B, the electronic portion of the analyzeris illustrated in block form. The electronic apparatus is described inmore detail in the copending application of Peter A. Howes, Ser. No.792,382, filed on Jan. 21, I969 now US. Pat. No. 3,650,149 entitledENGINE IGNITION AND POWER ANALYZER and assigned to the assignee of thisapplication. The electronic system requires the use of only seven inputconnections to the engine under test, including ground pickup 119. Leads120 and 121 are connected to the primary and secondary windings of theignition coil (not shown) to provide signals representative of theignition pulses induced across the primary and secondary windings,respectively. A battery voltage lead 122 and a current lead 123 areprovided for obtaining signals representing the battery terminal voltageand battery current. A vacuum pickup lead 124 is connected to a vacuumtransducer (not shown) coupled tothe engine manifold to provide a signalrepresentative of the manifold vacuum. A lead 125 is connected to thenumber one spark plug to provide pulses representative of the firingtimes for the number one.

cylinder.

A horsepower lead 126 and a tachometer lead 127 are connected-to adynamometer (not shown) which may be of a conventional type to providesignals representative of the horsepower. delivered at the rearwheels'of an automobile, and road speed, respectively. The signalssupplied on lead 126 need not be representative of the horsepower outputbut may be representative of any desired performance characteristic suchas torque, etc.. Leads 128, 129 and 130 are connected to a suitable gasanalyzer (not shown) to provide signals representative of the nitricoxide, carbon monoxide and hydrocarbon content of the engine exhaust.The signals from the leads 122-124 and 126-130 are coupled to the signalinput circuits of the three test meters described in more detail. Thesix possible meter scales are numbered 1-6, 7-12 and 13-18 for meters 1,2 and 3, respectively. The meter scale which is used to provide ameasure of the tested parameter is noted on the drawing and can bereadily correlated with the program switch position in the chart onpages 17 and 18. The output signals on certain of the leads 120-130 arealso coupled to the signal input circuit of the oscilloscope via theprogram switch.

The oscilloscope sweep voltages are initiated by theprimary or thesecondary ignition signals selected by thetrigger switch 13 and appliedby the programswitch 24 to a pulse shaper 132. The pulses on line 132are applied vialine 133 to a servo sweep generator 136. The

pulse shaper 132 (FIG. 6B) converts each ignition 6 P se to a narrowSquare W P l w shtrisset ihs.

servo sweep generator 136 to provide a ramp voltage ofeonstant amplitudeindependent of the pulse repetition rate. A level trigger 140 detects apredetermined amplitude in the output ramp .voltage from the generator136 and produces an output signal on line 141 in response thereto whichprecedes or anticipates the ignition pulse of the next cylinder to fire.The output signal on line 141 is applied by the program switch to asecond servo sweep generator 142 to provide a superimposed raster forthe oscilloscope, that is, a sawtooth sweep signal of constant amplitudewhich is synchronized with each output signal from the level trigger140, i.e., the ignition in each cylinder. In this mode, the rasterresults in the display of the primary or secondary ignition signals ineither a superimposed pattern or in a vertical stacked pattern as isdescribed in more detail in the copending application Ser. No. 792,382.

To provide a parade raster in which thespark plug voltages, for example,are displayed in a horizontally stacked pattern on the oscilloscope, theparade sweep trigger 144 is connected between the line 141 and anadditional stationary contact of the program switch 24. The parade sweeptrigger 144 includes an additional input via line 153 from a cylindershorting signal generator 150 which may be in the form of a ring counterhaving stages equal in number to the cylinders of the engine under.test. The cylinder shorting signal generator provides a square waveoutput signal on output line 151 in advance of or anticipatory of theignition tiring signal of a selected cylinder for repressing theignition of the selected cylinder as is described in more detail incopending application Ser. No. 792,382. The output signal from thegenerator 151 which is applied to the parade sweep trigger 144 by line153 is the anticipatory firing signal for cylinder No. l. The paradesweep trigger includes a gate which passes only the output signals fromlevel trigger which are coincident with ignition in the No. 1 cylinder.Thus the trigger 144 supplies one input pulse to the servo sweepgenerator 142 for each cycle of the engine. The resulting output sweepvoltage from the sweep generator 142 brackets the firing intervals ofall cylinders during one complete cycle for displaying ignition signalsin a horizontally stacked or parade pattern.

The point open trigger 138 receives as one input the signal from sweepgenerator 136 and another input from the secondary ignition lead 121 viathe pulse shaper 132. The output from the point open trigger 138 is asquare wave pulse delayed to coincide with the point opening times foreach cylinder. Thus instead of starting the sweep just prior to the timethe points are closed, the sweep of the oscilloscope is started when thepoints are opened. The point opening wave forms are displayed in avertical parade or superimposed pattern.

The program switch 24 applies one of three trigger pulses to the servosweep generator 142 to provide one of three possible sweep rasters,e.g., a ramp voltage synchronized with and slightly in advance of eachcylinder ignition. A ramp voltage synchronized with and slightly inadvance of each No. 1 cylinder ignition and a ramp voltage synchronizedwith each point opening transition. The three possible sweep voltagesare illustrated above the output line 143 of servo sweep genera- (leveltrigger 140 connected directly to generator 142), P represents theparade sweep (trigger 144) and R0. represents the point open sweep(point open trigger 138).

Either the primary or secondary ignition waveform may be applieddirectly to the vertical deflection coil of the oscilloscope via line145 through the program switch 24 to provide a superimposed orhorizontally stacked display. A vertically stacked display of theprimary or secondary ignition waveform is obtained by means of a mixer147. The mixer 147 receives a stair step signal having a number ofvoltage increments or steps equal to the number of cylinders of theengine under test from the stair step signal generator 134 when theprogram switch is rotated to provide a vertical parade pattern. Thestair step signal generator may be of the type discussed in copendingapplication Ser. No. 792,382 in which a ring counter having a number ofstages equal to the number of cylinders under test is advanced by eachfiring pulse from line 133. The output of the various stages of the ringcounter may be connected to ground through weighted resistors to providea stair step output voltage in a well known manner. The stair stepsignal generator 134 is reset by pulses from the No. 1 cylinder pickup,via line 152.

To measure the power contribution of each cylinder, the generator 150 isprovided to generate anticipatory shorting signals to short out thepoints and thereby repress the ignition of a selected cylinder so thatthe engine RPM drop for each shorted cylinder may be noted. Thegenerator 150 may be in the form ofa ring counter having,for example, 8stages as is illustrated in copending application Ser. No. 792,382. Thering counter counts the output signals from the level trigger 140 andprovides square wave output signals on line 151 which bracket the firingtimes of the selected cylinder. The cylinder select switch 32 is rotatedto select the cylinder to be shorted. The cylinder shorting signalgenerator also receives an input from the power switch 26 whichdetermines the number of operative stages of the ring counter inaccordance with the number of cylinders in the engine under test. Thefour stages of the ring counter will be utilized for a four cylinderengine, etc. The ring counter may be reset by pulses from the No. 1cylinder pickup via line 152.

To determine the dwell time of the points, the output signal from thetrigger switch 131 is applied by a low pass filter and clipper 155 vialine 156 through the program switch to an integrator 157. The outputsignal from the filter and clipper 155 is in the form ofa square wavehaving a duration proportional to the interval that the points areclosed. The integrator 157 provides a dc. output signal through anadjustable gain amplifier 158 to the dwell meter or the input signalcircuit of meter 1, scale No. 3, when the program switch is in positionC. The gain of the amplifier 158 is controlled by the power switch 26 inaccordance with the number of cylinders of the engine under test. Forexample, the feedback resistance of the amplifier 158 may be varied in aconventional manner to control the amplification of the signal appliedto the dwell meter and provide a meter movement representative of thepercentage of dwell time of the points.

The timing advance of the engine ignition is determined by applying theoutput from the sweep generator 136 to a variable level trigger 160which provides an output signal to a multivibrator 161 when the level ofthe ramp voltage from the generator 136 reaches a value determined by avoltage adjust circuit 163 which may be a potentiometer. The voltageadjust circuit 163 .is controlled by the manually operated knob 36 onthe strobe unit 34 by turning the knob 36 until the strobe lightcoincides with the engine timing mark. The setting of the voltage adjustpotentiometer 163 provides a dc. output signal which is applied throughthe program switch to the advance meter or meter 2, scale No. 8, whenthe program switch is in position C. The output of the multivibrator 161is applied through a strobe switch 165 to fire the strobe light 166.

The strobe switch 165 may be conveniently actuated by the knob 36 whenthe voltage adjust circuit 163 is at the end of its adjustment.Actuation of the switch 165 applies narrow square wave pulses from theNo. 1

cylinder via pulse shaper 168 to the strobe light. When the strobe light166 is actuated by the No. 1 cylinder firing pulse, the position of theengine advance is read in the conventional manner by means of a fixedscale on the engine block. The engine advance can be read either by theconventional method of illuminating the engine reference mark with theNo. 1 cylinder ignition pulse or by controlling the time that the strobeis fired by means of the voltage adjustment potentiometer 163 until theilluminated mark is aligned with a fixed reference corresponding withthe top dead center position of one of the pistons such as the numberone piston.

Engine speed is derived from an RPM signal genera- 5 tor 170 whichreceives pulses from the No. 1 cylinder pickup via line 152 and providesa dc output signal proportional to the repetition rate of such pulses orengine speed. The output of the RPM signal generator 170 is applied viathe program switch to meters 1 or 3 0 depending upon the position of theswitch as is illustrated in the chart on pages 17 and 18. An expand RPMsignal generator 172 is connected to the output of the RPM signalgenerator 170 for comparing the engine RPM as each cylinder is shortedwith the engine speed prior to cylinder shorting. The expand RPMgenerator 172 stores a signal representative of the engine speed priorto the activation of the cylinder select switch 32. When the cylinderselect switch is operated to short out a selected cylinder, the expandRPM generator is also activated via line 173 and compares the storedsignal with the new output of the RPM signal generator to provide anoutput to the RPM meter (meter 2, Scale No. 9) through program switch 24which is representative of the actual drop in engine RPM as eachcylinder 5 is shorted.

The following chart identifies each scale on the meters l, 2 and 3 andthe oscilloscope sweep raster for each program switch position.

Scales Oscilloscope Switch position Meter 1 Meter 2 Meter 3 RasterPattern l 7 l3 Superimposed Squashed primary. 2 7 l4 Parade Alternator.3 8 l4 Superimposed Primary. 3 8 l4 o Secondary. 3 9 l4 Parade 15/30 KVpn'./sec. 4 9 14 Pts. open Secondary vertical parade. l0 l5 SuperimposedSecondary. 5 11 I6 Parade Secondary vertical parade. 6 17 ..do SecondarylSKV. 6 l2 l7 Superimposed Secondary. 2 7 l5 Parade Alternator. 2 7 18None Meter scales for meters 1, 2 and 3 are as shown below:

METER l SCALE No. l o AMPs 500 2 0 [WM 120 20 3 I 0 DWELL 90 4 0 EngineIdle Speed 1200 RPM 5 o VACUUM 30 6 0 HC 1500 RPM METER 2 SCALE NO. 7 0VOLTAGE 20 volts 8 0 ADVANCE 90 9 0 RPM CHANGE 400 10 0 co 10% ll 0 ROADsPEEo I00 MPH l2 0 No 5000 RPM METER 3 SCALE No. l3 0 VOLTAGE DROP 2volts l4 0 ENGINE SPEED 5000 RPM 15 o ENGINE SPEED 10000 RPM 16 0 ROADHORSEPOWER 200 I7 0 RoAosPEED 100 MPH l8 0 OHMMETER a In position A theengine is tested for starter current via lead 123 and battery terminalvoltage via lead 122 when the engine is turned over by the starter andthe values of such parameters are read on meter 1 and 2. Theoscilloscope displays the squashed primary voltage waveform since theprimary winding is shorted to ground through an appropriate resistorduring the cranking test. The voltage drop across the ignition primarypoints with the points closed may also be measured on meter 3. i

In position B, the performance of the alternator or generator is testedand may be read on meter 3 after the cranking test is completed sincethe battery has been discharged during thecranking test. The outputcurrent of the alternator is read on meter 1, via lead 123 with theengine speed set, for example, at 2,500 RPM on meter -3. The batteryterminal voltage is again read on meter 2 and the scale for this meterhas remained unchanged. The alternator output voltage waveform isdisplayed on the oscilloscope.

In position C the basic ignition tests are performed. The dwell time indegrees of cylinder travel is read on meter 1 via amplifier output 158with the engine speed set at about 800 RPM on meter 3. The basic timingis In test position D, the waveforms of the secondary ignition pulsesare displayed in superimposed pattern on the oscilloscope to permit theoperator to identify a particular type of ignition problem, for example,wide gap, open circuits, series resistance, fouled plugs, etc.. Themeter scales have not changed from the previous position.

With the program switch in position E, the primary 'or secondaryignition waveforms are displayed on the oscilloscope in a horizontalparade pattern. At this time, the voltage requirements for each plug inengine firing order from left to right on the oscilloscope may be notedby the operator. Faulty spark plugs may be readily detected. The entireignition system output may be tested by use of the 30KV scale positionon the oscilloscope by means of a switch (not shown). Only the scale ofmeter 2 is changed in position E to read RPM change. In this position orin position F, the cylinder balance test may be made by shorting out onecylinder at a time .by means of the cylinder select switch 32 and notingthe RPM change on meter 2.

When the program switch is turned to position F, the oscilloscopedisplays the waveform of the secondary ignition pattern in firing orderfrom top to bottom in a vertical parade. In this position, the scoperaster will be the point open sweep discussed previously, and the stairstep signal generator 134 will be connected by the program switch to themixer 147 to provide the vertical stacked pattern on the oscilloscope.In position F, the scale of meter 1 is changed to scale No. 4 showingengine idle speed.

In position G, the program switch changes the scales of meters 1, 2 and3 to scales Nos. 5, 10 and 15 and connects the vacuum lead 124, thecarbon monoxide monitor lead 129 and the RPM generator to the signalinput circuits of meters 1, 2 and 3 respectively. The oscilloscope isprovided with the superimposed sweep and the secondary ignition pulsesare displayed thereon in a superimposed pattern. The carburetion systemis tested in this position either dynamically (by use of a dynamometer)or under a free running condition.

Turning the program switch to position H changes the scales to Nos. 11and 16 on meters 1 and 2, respectively to provide a measurement of roadspeed and road horsepower. The sweep raster is the parade mode and thesecondary ignition pulses are displayed in a vertical parade with thestair step signal generator 134 providing vertical separation of theignition pulses. In this position, the road horsepower at given enginespeeds may be determined.

In position J, the scales of the meters are changed as illustrated inthe above;c hart so thgttnctgtl P 'QYid a reading of the hydrocarboncontent and of the exhaust gases and meter 2 measures the carbonmonoxide content. Meter 3 provides a measurement of road speed bycoupling the dynamometer tachometer lead 127 to the signal input circuitof meter 3. In position J, the oscilloscope is provided with the paraderaster and the secondary ignition pulses are displayed in a horizontallyseparated pattern. If desired, the on time of the solenoid orhydraulically actuated fuel injector valves of fuel injector engines mayalso be monitored ID in position J. To monitor the additional parametersrequires the use of additional coupling probes for providing signalsrepresentative of the time that the fuel injector valves are open. Theon time of such valves may be displayed on the oscilloscope in asuperimposed pattern (with two valves generally being monitored at onetime).

In position K, only the scale of meter 2 changes to permit the operatorto determine the nitric oxide content of the engine exhaust. Theoscilloscope is provided 20 with a superimposed sweep signal and thesecondary ignition pulses are displayed in a superimposed pattern.

In switch position L, the performance of the charging system of theengine is again measured. The engine has been run at accelerated speedsduring the previous tests and the battery should be at a state of chargereflecting the voltage regulator setting. The alternator waveform isdisplayed on the oscilloscope by a parade raster with the engine runningat a given RPM. The a]- ternator voltage output should be in the form offlattened humps. Each of the meter scales is changed in switch positionL with meter 1 connected to read charging current in amperes on scaleNo. 2. Meter 2 is connected to read battery terminal voltage on scaleNo. 7 and meter 3 is connected to the RPM signal generator 170 toprovide a reading of engine speed.

Position M of the program switch changes only on the scale of meter 3 topermit the resistance of spark plug wires, etc., to be measured in ohms.The oscilloscope is not utilized in this position.

Many modifications to the preferred embodiment of this invention will beapparent to those skilled in the art. For example, the number ofselectable scale meters is a matter of choice. Two such meters willprovide considerable latitude in setting up testing procedures. Thetesting procedures programmed into the switch 24 may, of course, bevaried. Furthermore, the selectable scale meters may be modified, forexample, by the use I of one motor to first drive the drum to position aselected scale and then drive the tape to provide a measure of the inputsignal. The number of fixed and movable contacts on the program switchmay be varied to accommodate the measurement and display of more or lessengine parameters. The electronic system for generating the sweep andcylinder shorting signals may also be modified.

There has thus been described a unique electronic analyzer for internalcombustion engines which provides highly accurate measurement of engineparameters by relatively unskilled personnel.

What is claimed is:

1. In an apparatus for analyzing the operation of a multiple cylinderinternal combustion engine, the combination which comprises:

a plurality of probe pickup leads adapted to be coupled to the engine toprovide output signals representative of engine performancecharacteristics;

an oscilloscope having a signal input circuit and a sweep input circuit;sweep signal generating means for selectively generating one of aplurality of sweep voltages;

at least one selectable scale test meter having a test signal inputcircuit, an indicator movable between two points in response to thesignal applied to the input circuit to provide a measure of said inputsignal, a rotatable drum having a plurality of individual scales spacedaround the periphery thereof with one scale positioned adjacent theindicator and between the two points at a time, a scale selectioncircuit and means responsive to signals applied to the scale selectioncircuit for rotating the drum to position a selected scale adjacent theindicator; multiple position program switch having at least first,second and third contact means, the first contact means being coupledbetween selected probe pickup leads and the test input circuit of themeter for applying input signals to the meter representative ofpredetermined engine characteristics at selected switch positions, thesecond contact means being coupled between selected probes and thesignal input circuit of the oscilloscope to provide a display of signalsrepresentative of the selected probe pickup output signals for selectedswitch positions;

means including the third contact means for connecting the sweepgenerating means to the sweep input circuit of the oscilloscope andcontrolling the sweep output voltage to provide a selected sweep rasteron the oscilloscope for each switch position, the program switch beingarranged to provide simultaneous operation of the first, second andthird contact means; and

scale selector means responsive to each position of the program switchfor applying signals to the meter scale selection circuit for causingthe drum to position a selected scale adjacent the indicator for eachswitch position.

2. The combination as defined in claim 1 wherein the indicator is areference mark on a flexible member and the test meter includes meansfor moving the flexible member across one side of the drum in responseto the signal appliedto the inp ut circuit of the meter.

3. The combination as defined in claim 2 wherein the means for movingthe flexible member is a servo mechanism.

4. The combination as defined in claim 1 including a second selectablescale test meter having a test signal input circuit, an indicatormovable between two points in response to the signal applied to theinput circuit to provide a measure of said input signal, a rotatabledrum having a plurality of individual scales spaced around the peripherythereof with one scale positioned adjacent the indicator and between thetwo points at a time, a scale selection circuit and means responsive tosignals applied to the scale selection circuit for rotating the drum toposition a selected scale adjacent the indicator, and wherein theprogram switch includes fourth contact means, the fourth contact meansbeing coupled between selected probes and the test input circuit of thesecond meter for applying input signals to the meter representative ofthe output signals from individual probes at selected switch positionsand further including means responsive to each position of the programswitch for applying signalstothe meter scale selector circuit of thesecond meter for causing the drum to position a selected scale adjacentthe indicator for each switch position. i

5. The combination as defined in claim 1 wherein the scale selectormeans comprises a source of potential and an additional contact means ofthe program switch, the additional contact means being connected betweenthe source of potential and the scale selection circuit for applyingpredetermined signals to the scale selection circuit for each switchposition.

6. The combination as defined in claim 5 wherein each contact meanscomprises a stationary contact associated with each switch position anda rotatable contact which engages one stationary contact for each switchposition.

7. The combination as defined in claim 6 wherein the meter scaleselection circuit comprises a motor and a solenoid actuated indexingmember rai r'iiiii kiie drum to position the selected scale.

8. The combination as defined in claim 7 including a dynamometer coupledto the engine and having at least two output circuits for providingsignals representative of speed and engine performance characteristicand wherein the third and fourth contact means couples the outputsignals from the dynamometer to the signal input circuits of the firstand second meters at selected positions of the program switch.

9. The combination as defined in claim 6 including a gas analyzercoupled to the engine exhaust for providing output signalsrepresentative of the quantities of selected gases and wherein the firstand fourth contact means couple the output signals of the gas analyzerto the test signal input circuits of the first and second meters for aselected switch position.

10. The combination as defined in claim 6 including a cylinder selectswitch having a switch position for each cylinder of the engine undertest and means responsive to the position of the cylinder select switchfor opening the ignition in the selected cylinder.

11. In an apparatus for analyzing the operation of a multiple cylindercombustion engine provided with an ignition coil having a primary andsecondary winding, a starter, a battery, and a generating system, thecombination which comprises:

an ignition probe pickup means adapted to be cou pled to the primaryand/or secondary winding for providing signals representative of theignition firing pulses,

a battery voltage probe pickup for providing a signal representative ofthe battery terminal voltage,

a battery current pickup for providing a signal representative ofbattery current,

a cylinder number one pickup probe for providing a signal representativeof the ignition time of the number one cylinder,

an oscilloscope having a signal input circuit and a sweep input circuit,

sweep signal generating means for selectively generating one of aplurality of sweep voltages,

first and second selectable scale test meters, each meter having a testsignal input circuit, an indicator movable between two points inresponse to the sig nal applied to the input circuit to provide ameasure of the input signal, a rotatable drum having a plurality ofindividual scales spaced around the periphery thereof with one scalepositioned adjacent the indicator and between the two points at a time,

a scale selection circuit and means responsive to signals applied to thescale selection circuit for rotating the drum to position a selectedscale adjacent the indicator,

a multiple position program switch having first, second, third, fourth,fifth and sixth contact means, the first and second contact means beingcoupled between the test input circuits of the first and second metersand selected ones of the probe pickups for applying input signals to themeters representative of predetermined engine characteristics atselected switching positions,

means including the third and fourth contact means for applying signalsto the scale selection circuits of the first and second meters to rotatethe drums thereof to position a selected scale adjacent the respectiveindicators for each switch position, v

means connecting the fifth contact means in series relationship betweenselected probe pickups and the signal input circuit of the oscilloscopeto provide a display of signals representative of the selected probeoutput signals for selected switch positions,

means including the sixth contact means for connecting the sweep inputcircuit of the oscilloscope to the sweep input circuit of theoscilloscope and for applying a selected sweep voltage thereto for eachswitch position.

12. The combination as defined in claim 11 wherein each of the first,second, third, fourth, fifth and sixth contact means comprise aplurality of fixed contacts and a rotating contact which sequentiallyengages one stationary contact for each switch position.

13. The combination as defined in claim 12 including a dynamometercoupled to the engine and having at least two output circuits forproviding signals representative of speed and performance characteristicand wherein the first and second contact means couple the output signalsfrom the dynamometer to the signal input circuits of the first andsecond meters at a selected switch position of the program switch.

14. The combination as defined in claim 13 including a gas analyzercoupled to the engine exhaust and having three output signalsrepresentative of the hydrocarbon, carbon monoxide and nitric oxidecontent of the exhaust gas and wherein the first and second contactmeans couple the output signals from the exhaust gas analyzer to thesignal input circuits of the first and secr!!!9 2st?etas sstsstm tiqasqthe qg m sw 15. The combination as defined in claim 13 wherein the firstand second contact means couple the battery voltage and current probesto the signal input circuits of the first and second test meters at oneswitch position.

16. The combination as defined in claim 15 including pulse shaping andintegrating means for providing a dwell signal proportional to the dwelltime of the points and wherein the first or second contact means couplessaid dwell signal to the test input circuit of one of the first andsecond test meters at a selected switch position.

17. The combination as defined in claim 16 including means for providinga signal representative of the igni' tion advance and wherein the firstor second contact means couples the advance signal to the test inputcircuit of the first or second meter at a selected switch position.

18. The combination as defined in claim 12 wherein the engine includes adistributor with points which close and open to provide the ignitionpulses and wherein the sweep signal generating means selectivelygenerates a first sweep voltage synchronized with each cylinderignition, a second sweep voltage synchronized with each ignition incylinder number one and a third sweep voltage synchronized with thepoint opening transition for each cylinder.

19. The combination as defined in claim 12 including a gas analyzercoupled to the engine exhaust and having three output signalsrepresentative of the hydrocarbon, carbon monoxide and nitric oxidecontent of the exhaust gas and wherein the first and second contactmeans couple the output signals from the exhaust gas analyzer to thesignal input circuits of the first and second meters at selectedpositions of the program switch.

20. The combination as defined in claim 12 wherein the first and secondcontact means couple the battery voltage and current probes to thesignal input circuits of the first and second test meters at one switchposition.

21. The combination as defined in claim 11 wherein the indicator is areference mark on a flexible member and the test meter includes meansfor moving the flexible member across one side of the drum in responseto the signal applied to the input circuit of the meter.

22. The combination as defined in claim 21 wherein the flexible memberis a tape having a transparent portion and a colored portion with thetransition between the two portions forming the indicator.

23. The combination as defined in claim 22 wherein the means for movingthe tape past the drum includes a motor and a reel connected to themotor for winding or unwinding one end of the tape thereon, meansresponsive to the shaft position of the motor for providing a shaftposition signal representative of the motor shaft position and meansresponsive to the difference signal between the test signal and theshaft position signal of a respective test meter for controlling themotor.

24. In an apparatus for analyzing the operation of a multiple cylinderinternal combustion engine, the combination which comprises:

a plurality of probe pickup leads adapted to be coupled to the engine toprovide output signals representative of engine performancecharacteristics;

an oscilloscope having a signal input circuit and a sweep input circuit;

sweep signal generating means for selectively generating one of aplurality of sweep voltages;

at least one selectable scale test meter having a test signal inputcircuit, an indicator movable between two points in response to thesignal applied to the input circuit to provide a measure of said inputsignal, a moveable scale member carrying a plurality of individualspaced scales thereon with one scale positioned adjacent the indicatorand between the two points at a time, a scale selection circuit andmeans responsive to signals applied to the scale selection circuit formoving the scale membertgposition a selected scale adjacent theindicator; multiple position program switch having at least first,second and third contact means, the first contact means being coupledbetween selected probe pickup leads and the test input circuit of themeter for applying input signals to the meter representative ofpredetermined engine characteristics at selected switch positions, thesecond contact means being coupled between selected probes and thesignal input circuit of the oscilloscope to provide a display of signalsrepresentative of the selected probe pickup output signals for selectedswitch positions; means including the third contact means for connectingthe sweep generating means to the sweep input circuit of theoscilloscope and controlling the sweep output voltage to provide aselected sweep raster on the oscilloscope for each switch position; andscale selector means responsive to each position of the program switchfor applying signals to the meter scale selection circuit for causingthe scale member to position a selected scale adjacent the V indicatorfor each switch position. v 25. The combination as defined in claim 24including a second selectable scale test meter and wherein the programswitch includes fourth contact means, the fourth contact means beingcoupled between selected probes and the test input circuit of the secondmeter for applying input signals to the meter representative of theoutput signals from individual probes at selected switch positions andfurther including means responsive to each position of the programswitch for applying signals to the meter scale selector circuit of thesecond meter for causing the scale member to position a selected scaleadjacent the indicator for each switch position.

26. The combination as defined in claim 25 including a third selectablescale test meter and wherein the program switch includes fifth contactmeans, the fifth contact means being coupled between selected probes andthe test input circuit of the third meter for applying input signals tothe meter representative of the output signals from individual probes atselected switch positions and further including means responsive to eachposition of the program switch for applying signals to the meter scaleselector circuit of the third meter for causing the scale member toposition a selected scale adiasa ll g 92 199 95 qtsa hwjish pqs ti w-27. The combination as defined in claim 25 wherein the movable scalemember of each meter is a drum having a plurality of scales positionedaround the periphery tberL e 28. The combination as defined in claim 27wherein each contact means comprises a stationary contact associatedwith each switch position and a rotatable contact which engages onestationary contact for each switch position.

1. In an apparatus for analyzing the operation of a multiple cylinderinternal combustion engine, the combination which comprises: a pluralityof probe pickup leads adapted to be coupled to the engine to provideoutput signals representative of engine performance characteristics; anoscilloscope having a signal input circuit and a sweep input circuit;sweep signal generating means for selectively generating one of aplurality of sweep voltages; at least one selectable scale test meterhaving a test signal input circuit, an indicator movable between twopoints in response to the signal applied to the input circuit to providea measure of said input signal, a rotatable drum having a plurality ofindividual scales spaced around the periphery thereof with one scalepositioned adjacent the indicator and between the two points at a time,a scale selection circuit and means responsive to signals applied to thescale selection circuit for rotating the drum to position a selectedscale adjacent the indicator; a multiple position program switch havingat least first, second and third contact means, the first contact meansbeing coupled between selected probe pickup leads and the test inputcircuit of the meter for applying input signals to the meterrepresentative of predetermined engine characteristics at selectedswitch positions, the second contact means being coupled betweenselected probes and the signal input circuit of the oscilloscope toprovide a display of signals representative of the selected probe pickupoutput signals for selected switch positions; means including the thirdcontact means for connecting the sweep generating means to the sweepinput circuit of the oscilloscope and controlling the sweep outputvoltage to provide a selected sweep raster on the oscilloscope for eachswitch position, the program switch being arranged to providesimultaneous operation of the first, second and third contact means; andscale selector means responsive to each position of the program switchfor applying signals to the meTer scale selection circuit for causingthe drum to position a selected scale adjacent the indicator for eachswitch position.
 2. The combination as defined in claim 1 wherein theindicator is a reference mark on a flexible member and the test meterincludes means for moving the flexible member across one side of thedrum in response to the signal applied to the input circuit of themeter.
 3. The combination as defined in claim 2 wherein the means formoving the flexible member is a servo mechanism.
 4. The combination asdefined in claim 1 including a second selectable scale test meter havinga test signal input circuit, an indicator movable between two points inresponse to the signal applied to the input circuit to provide a measureof said input signal, a rotatable drum having a plurality of individualscales spaced around the periphery thereof with one scale positionedadjacent the indicator and between the two points at a time, a scaleselection circuit and means responsive to signals applied to the scaleselection circuit for rotating the drum to position a selected scaleadjacent the indicator, and wherein the program switch includes fourthcontact means, the fourth contact means being coupled between selectedprobes and the test input circuit of the second meter for applying inputsignals to the meter representative of the output signals fromindividual probes at selected switch positions and further includingmeans responsive to each position of the program switch for applyingsignals to the meter scale selector circuit of the second meter forcausing the drum to position a selected scale adjacent the indicator foreach switch position.
 5. The combination as defined in claim 1 whereinthe scale selector means comprises a source of potential and anadditional contact means of the program switch, the additional contactmeans being connected between the source of potential and the scaleselection circuit for applying predetermined signals to the scaleselection circuit for each switch position.
 6. The combination asdefined in claim 5 wherein each contact means comprises a stationarycontact associated with each switch position and a rotatable contactwhich engages one stationary contact for each switch position.
 7. Thecombination as defined in claim 6 wherein the meter scale selectioncircuit comprises a motor and a solenoid actuated indexing member forrotating the drum to position the selected scale.
 8. The combination asdefined in claim 7 including a dynamometer coupled to the engine andhaving at least two output circuits for providing signals representativeof speed and engine performance characteristic and wherein the third andfourth contact means couples the output signals from the dynamometer tothe signal input circuits of the first and second meters at selectedpositions of the program switch.
 9. The combination as defined in claim6 including a gas analyzer coupled to the engine exhaust for providingoutput signals representative of the quantities of selected gases andwherein the first and fourth contact means couple the output signals ofthe gas analyzer to the test signal input circuits of the first andsecond meters for a selected switch position.
 10. The combination asdefined in claim 6 including a cylinder select switch having a switchposition for each cylinder of the engine under test and means responsiveto the position of the cylinder select switch for opening the ignitionin the selected cylinder.
 11. In an apparatus for analyzing theoperation of a multiple cylinder combustion engine provided with anignition coil having a primary and secondary winding, a starter, abattery, and a generating system, the combination which comprises: anignition probe pickup means adapted to be coupled to the primary and/orsecondary winding for providing signals representative of the ignitionfiring pulses, a battery voltage probe pickup for providing a signalrepresentative of the battery terminal voltage, A battery current pickupfor providing a signal representative of battery current, a cylindernumber one pickup probe for providing a signal representative of theignition time of the number one cylinder, an oscilloscope having asignal input circuit and a sweep input circuit, sweep signal generatingmeans for selectively generating one of a plurality of sweep voltages,first and second selectable scale test meters, each meter having a testsignal input circuit, an indicator movable between two points inresponse to the signal applied to the input circuit to provide a measureof the input signal, a rotatable drum having a plurality of individualscales spaced around the periphery thereof with one scale positionedadjacent the indicator and between the two points at a time, a scaleselection circuit and means responsive to signals applied to the scaleselection circuit for rotating the drum to position a selected scaleadjacent the indicator, a multiple position program switch having first,second, third, fourth, fifth and sixth contact means, the first andsecond contact means being coupled between the test input circuits ofthe first and second meters and selected ones of the probe pickups forapplying input signals to the meters representative of predeterminedengine characteristics at selected switching positions, means includingthe third and fourth contact means for applying signals to the scaleselection circuits of the first and second meters to rotate the drumsthereof to position a selected scale adjacent the respective indicatorsfor each switch position, means connecting the fifth contact means inseries relationship between selected probe pickups and the signal inputcircuit of the oscilloscope to provide a display of signalsrepresentative of the selected probe output signals for selected switchpositions, means including the sixth contact means for connecting thesweep input circuit of the oscilloscope to the sweep input circuit ofthe oscilloscope and for applying a selected sweep voltage thereto foreach switch position.
 12. The combination as defined in claim 11 whereineach of the first, second, third, fourth, fifth and sixth contact meanscomprise a plurality of fixed contacts and a rotating contact whichsequentially engages one stationary contact for each switch position.13. The combination as defined in claim 12 including a dynamometercoupled to the engine and having at least two output circuits forproviding signals representative of speed and performance characteristicand wherein the first and second contact means couple the output signalsfrom the dynamometer to the signal input circuits of the first andsecond meters at a selected switch position of the program switch. 14.The combination as defined in claim 13 including a gas analyzer coupledto the engine exhaust and having three output signals representative ofthe hydrocarbon, carbon monoxide and nitric oxide content of the exhaustgas and wherein the first and second contact means couple the outputsignals from the exhaust gas analyzer to the signal input circuits ofthe first and second meters at selected positions of the program switch.15. The combination as defined in claim 13 wherein the first and secondcontact means couple the battery voltage and current probes to thesignal input circuits of the first and second test meters at one switchposition.
 16. The combination as defined in claim 15 including pulseshaping and integrating means for providing a dwell signal proportionalto the dwell time of the points and wherein the first or second contactmeans couples said dwell signal to the test input circuit of one of thefirst and second test meters at a selected switch position.
 17. Thecombination as defined in claim 16 including means for providing asignal representative of the ignition advance and wherein the first orsecond contact means couples the advance signal to the test inputcircuit of the first or second meter at a selected switch position. 18.The combination as defined in claim 12 wherein the engine includes adistributor with points which close and open to provide the ignitionpulses and wherein the sweep signal generating means selectivelygenerates a first sweep voltage synchronized with each cylinderignition, a second sweep voltage synchronized with each ignition incylinder number one and a third sweep voltage synchronized with thepoint opening transition for each cylinder.
 19. The combination asdefined in claim 12 including a gas analyzer coupled to the engineexhaust and having three output signals representative of thehydrocarbon, carbon monoxide and nitric oxide content of the exhaust gasand wherein the first and second contact means couple the output signalsfrom the exhaust gas analyzer to the signal input circuits of the firstand second meters at selected positions of the program switch.
 20. Thecombination as defined in claim 12 wherein the first and second contactmeans couple the battery voltage and current probes to the signal inputcircuits of the first and second test meters at one switch position. 21.The combination as defined in claim 11 wherein the indicator is areference mark on a flexible member and the test meter includes meansfor moving the flexible member across one side of the drum in responseto the signal applied to the input circuit of the meter.
 22. Thecombination as defined in claim 21 wherein the flexible member is a tapehaving a transparent portion and a colored portion with the transitionbetween the two portions forming the indicator.
 23. The combination asdefined in claim 22 wherein the means for moving the tape past the drumincludes a motor and a reel connected to the motor for winding orunwinding one end of the tape thereon, means responsive to the shaftposition of the motor for providing a shaft position signalrepresentative of the motor shaft position and means responsive to thedifference signal between the test signal and the shaft position signalof a respective test meter for controlling the motor.
 24. In anapparatus for analyzing the operation of a multiple cylinder internalcombustion engine, the combination which comprises: a plurality of probepickup leads adapted to be coupled to the engine to provide outputsignals representative of engine performance characteristics; anoscilloscope having a signal input circuit and a sweep input circuit;sweep signal generating means for selectively generating one of aplurality of sweep voltages; at least one selectable scale test meterhaving a test signal input circuit, an indicator movable between twopoints in response to the signal applied to the input circuit to providea measure of said input signal, a moveable scale member carrying aplurality of individual spaced scales thereon with one scale positionedadjacent the indicator and between the two points at a time, a scaleselection circuit and means responsive to signals applied to the scaleselection circuit for moving the scale member to position a selectedscale adjacent the indicator; a multiple position program switch havingat least first, second and third contact means, the first contact meansbeing coupled between selected probe pickup leads and the test inputcircuit of the meter for applying input signals to the meterrepresentative of predetermined engine characteristics at selectedswitch positions, the second contact means being coupled betweenselected probes and the signal input circuit of the oscilloscope toprovide a display of signals representative of the selected probe pickupoutput signals for selected switch positions; means including the thirdcontact means for connecting the sweep generating means to the sweepinput circuit of the oscilloscope and controlling the sweep outputvoltage to provide a selected sweep raster on the oscilloscope for eachswitch position; and scale selector means responsive to each position ofthe program switch for applying siGnals to the meter scale selectioncircuit for causing the scale member to position a selected scaleadjacent the indicator for each switch position.
 25. The combination asdefined in claim 24 including a second selectable scale test meter andwherein the program switch includes fourth contact means, the fourthcontact means being coupled between selected probes and the test inputcircuit of the second meter for applying input signals to the meterrepresentative of the output signals from individual probes at selectedswitch positions and further including means responsive to each positionof the program switch for applying signals to the meter scale selectorcircuit of the second meter for causing the scale member to position aselected scale adjacent the indicator for each switch position.
 26. Thecombination as defined in claim 25 including a third selectable scaletest meter and wherein the program switch includes fifth contact means,the fifth contact means being coupled between selected probes and thetest input circuit of the third meter for applying input signals to themeter representative of the output signals from individual probes atselected switch positions and further including means responsive to eachposition of the program switch for applying signals to the meter scaleselector circuit of the third meter for causing the scale member toposition a selected scale adjacent the indicator for each switchposition.
 27. The combination as defined in claim 25 wherein the movablescale member of each meter is a drum having a plurality of scalespositioned around the periphery thereof.
 28. The combination as definedin claim 27 wherein each contact means comprises a stationary contactassociated with each switch position and a rotatable contact whichengages one stationary contact for each switch position.